Digital valves are well known, and consist generally of a valve block with two sets of conduits which are interconnected by a plurality of orifices of various diameters. Solenoid operated plungers selectively open and close various combinations of the orifices, so as to control the total volume of fluid passing through the valve.
Digital valves have been widely used for controlling the drive of piston and cylinder assemblies. Usually a digital valve is provided in the supply line, and a separate digital valve is provided in the return line in order to control the return movement of the piston. Two additional digital valves must be provided to reverse the supply and return flows.
The above circumstances cause the operational cost to increase considerably, for it is necessary to control four separate and independent digital valves, thus increasing the complexity of the associated data processing equipment.
If control of the piston over both its forward and return stroke is required, this requires the addition of additional digital valves, which must be operated by corresponding logic circuits, further increasing the cost of the system, particularly when great accuracy or complex movements of the piston are required.
For long time there has been a need for a digital control valve which can control the return stroke of the piston in addition to controlling the forward stroke.